This invention relates to an automotive power seat assembly wherein an automotive seat reclining mechanism and seat rail means are driven by motors.
Hithertofore there has been known an automotive power seat assembly wherein the seat reclining mechanism and seat rail means are driven by motors. In the prior art power seat assembly, the rotation of the motors in the forward and reverse directions and the stoppage of the motors are controlled by switches or relays and when overload current flows through the motor or motors, the flow of current is interrupted by a bimetal circuit breaker. Furthermore, the operation range of the power seat assembly is regulated by a limit switch. In the prior art power seat assembly of the above type, a large type DC magnet motor or motors of high torque - low speed rotation which have high starting torque and are capable of withstanding overload in locking are employed.
The large type DC magnet motor employed in the prior art power seat assembly exhibits high heat resistance and has the characteristic of high torque (maximum of about 8 kg.cm) and low speed rotation (maximum of about 3500 rotations/min.) as shown in FIG. 4 and large magnetic flux as a stationary magnetic pole. The rotor in the magnet motor is of an eight-pole lap winding formed of a thick coil capable of withstanding high load at the time of starting and heat to be generated by large current in locking and sufficient mechanical strength. Thus, the prior art power seat assembly inevitably has such a large size that the assembly can not be incorporated into the seat structure of a small type automobile and is expensive because the motor has a surplus capacity. Furthermore, in the prior art power seat assembly, the rotation of the high torque - low speed motor is controlled by a switch or relay within the region shown by the slanting line in FIG. 4 and thus, when load torque varies substantially as the backrest of the power seat assembly is erected from its horizontal orientation, the rotational speed of the motor varies substantially depending upon the reclining angle of the backrest which presents the problem that smooth and pleasing operation of the power seat assembly can not be achieved. Furthermore, the region for rotating of the motor shown by the slanting line of FIG. 4 presents the problems that the operation efficiency is low, power in the power source mounted on the automobile is wasted and the motor generates a substantial amount of heat with large current due to overload. In addition, when a substantially reducing gear is employed in the prior art power seat assembly, although variation in rotational speed of the motor can be made small, there is the drawback that the rotational speed becomes too slow or the output torque is too high resulting in breakage of the driving component or components themselves when any trouble is present in the component or components.
Furthermore, in the prior art power seat assembly, large starting current flows through the motor at the time of starting and it takes a long time from the time when overload current begins to flow through the motor until the bimetal circuit breaker interrupts the flow of current through the motor and thus, the motor should be a large type and an expensive one which exhibits high heat resistance. In addition, in the prior power seat assembly, since a limit switch for regulating the operation range of the assembly is disposed on each driving portion of the assembly, there is the problem that the circuit wiring between the motor, control circuit and limit switch become complicated.